If doubt he's a cash millionaire. Maybe an asset one. But like with movie stars people guess net worth by adding up everything they've ever got paid and assume it's all accumulated in one lump, untouched sum the bank.
"He got $5m from that movie and $10m for that other movie, so he's got $15m in his account"
No, there'll be real estate, taxes, fees, staff, friends, family, lifestyle etc to fund and upkeep.
Dallas probably funds the lifestyle at quite a high end of several people around him and has for quite a few years now. He doesn't just get to squirrel the cash away and look at it like some untouchable and untouched museum exhibit. The holidays the homes, the cars... the lifestyle isn't free for him or his friends/family or close circle.
Not suggesting he's not extremely well off compared to most people but I think this is an example of where people vastly overestimate someone's solvency. If he liquidated all of his properties and assets I've no doubt he is a millionaire. But the guy isn't tycoon. He's made a lot and probably spent a lot and is doing pretty damn good comparable to most of us.
I doubt his pile of cash has sat there untouched though, and majority of his wealth is probably invested in his home and other assets as opposed to him being solvent to the extent he's borrowed Scrooge McDuck's diving board